KIEV, Ukraine -- A Ukrainian official said a passenger plane carrying 298 people, including three infants and 15 crew members, was shot down Thursday over a town in the east of the country, and Malaysian Airlines tweeted that it lost contact with one of its flights over Ukrainian airspace.
An Associated Press journalist counted at least 22 bodies at the wreckage site, which covers a wide area.
Anton Gerashenko says on his Facebook page the plane was flying at an altitude of 10,000 meters (33,000 feet) when it was hit Thursday by a missile fired from a Buk launcher.
A similar launcher was seen by Associated Press journalists near the eastern Ukrainian town of Snizhne earlier Thursday.
The United States Department of State cannot confirm at this time the number of American passengers on board.
Speaking at an event in Delaware Thursday, President Barack Obama addressed the crash.
"Our thoughts and prayers are with all the families of the passengers, wherever they call home," said the president.
Malaysia Airlines said on its Twitter feed that it lost contact of Flight 17, a Boeing 777, from Amsterdam to Kuala Lumpur Thursday.
Malaysia Airlines has lost contact of MH17 from Amsterdam. The last known position was over Ukrainian airspace. More details to follow.— Malaysia Airlines (@MAS) July 17, 2014
The region where the flight was lost has seen severe fighting between Ukrainian forces and pro-Russia separatist rebels in recent days.
Amateur cellphone video is circulating online though it has not been independently confirmed as being from the crash.
Malaysia's Minister of Defense Hishammuddin Hussein tweeted there is no confirmation the jet was shot down.
Reuters, however, is reporting militants shot down the jet, killing all 298 on board were lost. A correspondent claims to be at the crash site and reports burning wreckage and victims on the ground outside the plane.
Russian news agencies have quoted witnesses as saying they saw a plane being hit by what they thought was a rocket.
A U.S. official says that American intelligence authorities believe a surface-to-air missile took down the Malaysian passenger plane as it flew over eastern Ukraine Thursday.
Ukraine's president says his country's armed forces did not shoot at any airborne targets.
The official says the U.S. is still working to determine additional details about the crash, including who fired the missile and whether it came from the Russian or Ukraine side of the border. The official was not authorized to discuss the matter publicly so spoke on condition of anonymity.
President Petro Poroshenko says Thursday "we do not exclude that this plane was shot down, and we stress that the Armed Forces of Ukraine did not take action against any airborne targets."
Poroshenko said "we are sure that those who are guilty in this tragedy will be held responsible."
Separatist leader Andrei Purgin also denied shooting anything down but said he was certain Ukrainian troopers were responsible, though he gave no explanation for the statement.
Russian President Vladmir Putin says Ukraine bears responsibility for the crash of a Malaysian airliner.
A Kremlin statement early Friday said Putin opened a meeting with his economic advisers by calling for a moment of silence over the crash.
Then, he said, "This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeast Ukraine. And, certainly, the state over whose territory this occurred bears responsibility for this awful tragedy."
In a call with Poroshenko, President Obama emphasized that all evidence from the crash site must remain in place on the territory of Ukraine until international investigators are able to examine all aspects of the tragedy, according to a White House news release regarding the call.
On Wednesday evening, a Ukrainian fighter jet was shot down by an air-to-air missile from a Russian plane, Ukrainian authorities said Thursday, adding to what Kiev says is mounting evidence that Moscow is directly supporting the separatist insurgents. Security Council spokesman Andrei Lysenko said the pilot of the Sukhoi-25 jet hit by the air-to-air missile was forced to bail after his jet was shot down.
Pro-Russia rebels, meanwhile, claimed responsibility for strikes Wednesday on two Ukrainian Sukhoi-25 jets. The Ukrainian Defense Ministry said the second jet was hit by a portable surface-to-air missile, but added the pilot was unscathed and managed to land his plane safely
Moscow denies Western charges that is supporting the separatists or sowing unrest in its neighbor. The Russian Defense Ministry couldn't be reached for comment Thursday about the Ukrainian jet being shot down.
Earlier this week, Ukraine said a military transport plane was shot down Monday by a missile fired from Russian territory.
Aviation authorities in several countries, including the FAA in the United States, issued warnings not to fly over parts of Ukraine prior to the crash. Within hours, several international airlines announced they will avoid Ukrainian airspace.
This is the second time that a Malaysia Airlines plane had gone missing in less than six months. Malaysia Airlines Flight 370 disappeared in March while en route from Kuala Lumpur to Beijing. It has not been found, but the search has been concentrated in the Indian Ocean far west of Australia.
A local University of Tulsa Russian Politics professor gave insight on the recent issues, read more here.
NBC, Reuters and the Associated Press all contributed to this report.